Field of Invention
The present invention relates to wide area lighting systems which utilize a plurality of light fixtures for aerial lighting. In particular, the invention relates to methods and apparatus to provide direct illumination on aerial objects or to a volume of aerial space, to monitor chromatic and luminance contrast of the sky and provide either an illuminance of contrasting color or no illuminance to provide the spectral distribution that will provide the most contrast between an object such as a sports ball (e.g. baseball, softball, golf ball) and its background, including but not limited to a softball against the twilight sky and a golf ball against green grass, including the use of UV or near UV light and/or UV activated ink, paint, or other colorant to improve contrast and visibility of a ball, to control the direction and intensity of light to reduce glare for viewers within the target area, and to reduce glare and spill light outside the target area.
Background of Invention
Optimizing visibility of sports balls, with specific attention given to optimizing contrast of sports balls with reference to their backgrounds, is a matter of considerable discussion in the art. Wellington, in U.S. Pat. No. 7,444,770, which is incorporated by reference, discusses this and cites several references to industry studies. For purposes of this application, “optimizing” visibility and contrast refers to techniques, methods, etc. that improve visual acquisition, recognition, differentiation, or tracking of an object such as a ball in flight.
Baseball or softball games often will begin during late afternoon when lighting is good, and continue through twilight and into nighttime hours. This presents a challenge for lighting during the twilight transition, since during sunset lighting conditions change dramatically. Just prior to and after sunset, there is a period of time when there is very little, if any, contrast between the sky and the ball. During the day, the sky typically will be quite bright, so that an airborne ball viewed from below will appear dark in comparison to the sky. This means that there is sufficient contrast to easily see the ball. Likewise, when the sun has fully set and the sky is dark, it does not take much illuminance on a ball in the air in order for the ball to have a sufficient luminance against the dark sky, so that again, there is sufficient contrast to see the ball. However, at some point during the transition from daylight to night, the ball and the sky will have nearly the same luminance, and often the color of the ball provides little chromatic contrast against the sky resulting in very little visual contrast. This makes the ball more difficult to see, reducing “playability.” Unfortunately, because of factors that will be outlined below, the use of aerial lighting during this transitional period may not always help, and sometimes may even cause a reduction in the visual contrast.
The sky during a typical sunset will have areas of high luminance that, though greatly reduced from daylight brightness, is still much brighter than the light that can be provided by artificial aerial lighting. Some areas will have a luminance approximately equal to the luminance that can be provided by aerial lighting. There will also be areas of low luminance that are close to night time levels. Colors may range from indigo and blue, to yellow, orange, rose, and pink, all within a single sunset. For best visual contrast, these different areas would require lighting that ranges from intense white in the darkest areas, to red, blue, green, or many other possible combinations of color in order to contrast with the colored background. But most sports field lighting operates as if there are only two sky conditions: day and night. Lights, which include both field lights and aerial lighting, can be off or on, but there is no ability to compensate for the twilight transition. And in most cases, since aerial lighting is often provided by directing light from the field lighting luminaires upwardly, as seen in FIG. 1B, where a single pole with lights is illustrated (typically there are plural such poles and lights), turning on the field lights automatically turns on the aerial lighting as well. This means that for some conditions (e.g. where aerial lighting is provided by the same source as field lighting), early twilight field lighting is detrimental to aerial visibility, but for other conditions later twilight field lighting is equally detrimental, since in both cases contrast, and therefore playability, can be reduced by providing the wrong lighting level.
FIGS. 1A and 1B show a simplified version of baseball field 10 with multiple light fixtures 110 on each pole 100, FIG. 1B with only one light pole shown for clarity. Real-world installations would have many poles and luminaires (e.g. see FIG. 1A), but the principles are the same as illustrated herein. Field lights 110 on pole 100 at field 10, FIG. 1B, provide field lighting in the areas between exemplary rays 51 and 52. This provides illumination of ball 20 when in the “ground zone” 40. Lights 110 also direct some light in the area between rays 52 and 53. This provides some useful illumination on ball 30 in the “fly zone” 50, but also directs unwanted light as exemplified by ray 54 towards off-field object 55, which could be a residential building, office, or other location which is harmed or adversely affected by having unwanted light illuminating the object. It can be appreciated then that using field lights mounted on a high pole to direct light in a broad angle that illuminates the fly zone, will of necessity direct some light off the field in an undesired direction, resulting in unwanted light on neighboring properties. So a better or alternative solution is needed or beneficial for at least some cases.
Another issue is the desire to save money in the operation of sports lighting. Since lighting a large sports field consumes a lot of electrical power, it is advantageous to reduce the number of hours of operation of a sports field lighting system. For instance, for a game anticipated to require 2.5 hours of lighting, delaying lighting operation by 15 minutes, by means of more precisely predicting the time when additional or alternative uplighting will contribute to playability, would reduce power usage for the evening by an estimated 10% which can result in significant savings. Even for a 5 hour period, delaying the start of aerial lighting by 15 minutes would generate a savings of 5%. In order to accomplish this “daylight harvesting,” lights may be turned on a set number of minutes before sunset. Or, a photocell or other sensor may be used to turn on lights in response to reduced light from the sky. However, since lighting conditions at sunset are not consistent, even though sunset time is known, there are some problems associated with this approach, since neither methodology necessarily ensures that aerial lighting will be turned on at the correct time for all sky conditions. Therefore, the aerial lighting might still be turned on too early, which could reduce rather than enhance visual contrast. Or the aerial lighting might be turned on too late for optimal contrast under some conditions.
Another problem with using field lights as a source of aerial lighting, assuming the use of HID lighting technology, is the fact that conventional HID lamps require several minutes of warm-up when turned on before they can effectively provide light, and once turned off require a cooling-off period before they can be re-lit. This means that to allow for adequate warm-up time, the lights normally need to be turned on before they are needed so that they will be on when needed. Also, they can't be turned off when not needed, since with changing conditions they could be needed before it is possible to get them turned on and warmed up in time.
Still another problem with this method is that it doesn't compensate for color. There is no known way to pre-program colored lights to match light conditions that can change not only daily, but even minute-by-minute. For example, it might seem to make sense to add illumination that has a spectral distribution that is weighted more towards blue wavelengths, since twilight illumination in the vicinity of the setting sun can be reddish in color. However most of the sky tends to remain blue even as the sun is setting, and therefore some sky conditions would benefit by adding yellow, rather than blue light. Under those conditions, adding blue light would reduce rather than improve contrast. So attempting to pre-define a color scheme for twilight lighting is likely to be difficult if not impossible.
There is therefore room for improvement in the art.